Heredocs can create Interpolated(X)StringNodes or (X)StringNodes (#1427)

Prior to this commit, heredocs were automatically InterpolatedNodes
regardless of whether there was actually interpolation. With this
commit, heredocs are only interpolate if there is actually
interpolation

Author: jemmaissroff

src/yarp.c

@@ -8,8 +8,12 @@ class HeredocDedentTest < TestCase
 
     File.read(filepath).split(/(?=\n)\n(?=<)/).each_with_index do |heredoc, index|
       define_method "test_heredoc_#{index}" do
-        parts = YARP.parse(heredoc).value.statements.body.first.parts
-        actual = parts.map { |part| part.is_a?(StringNode) ? part.unescaped : "1" }.join
+        node = YARP.parse(heredoc).value.statements.body.first
+        if node.is_a? StringNode
+          actual = node.unescaped
+        else
+          actual = node.parts.map { |part| part.is_a?(StringNode) ? part.unescaped : "1" }.join
+        end
 
         assert_equal(eval(heredoc), actual, "Expected heredocs to match.")
       end

test/yarp/heredoc_dedent_test.rb

@@ -460,7 +460,7 @@ def test_InterpolatedRegularExpressionNode
 
     def test_InterpolatedStringNode
       assert_location(InterpolatedStringNode, "\"foo \#@bar baz\"")
-      assert_location(InterpolatedStringNode, "<<~A\nhello world\nA", 0...4)
+      assert_location(InterpolatedStringNode, "<<~A\nhello \#{1} world\nA", 0...4)
     end
 
     def test_InterpolatedSymbolNode

test/yarp/location_test.rb

@@ -186,7 +186,11 @@ def assert_non_overlapping_locations(node)
         # We only want to compare parent/child location overlap in the case that
         # we are not looking at a heredoc. That's because heredoc locations are
         # special in that they only use the declaration of the heredoc.
-        compare = !(current.is_a?(InterpolatedStringNode) || current.is_a?(InterpolatedXStringNode)) || !current.opening&.start_with?("<<")
+        compare = !(current.is_a?(StringNode) ||
+                    current.is_a?(XStringNode) ||
+                    current.is_a?(InterpolatedStringNode) ||
+                    current.is_a?(InterpolatedXStringNode)) ||
+        !current.opening&.start_with?("<<")
 
         current.child_nodes.each do |child|
           # child_nodes can return nil values, so we need to skip those.